Method of preparing superhydrophobic asphalt

ABSTRACT

A superhydrophobic asphalt and a method of its preparation. The superhydrophobic asphalt contains an asphalt layer containing a polymer modified asphalt, preferably a radial SBS modified asphalt, and a polypropylene layer. The polypropylene layer comprises granules of polypropylene thermally fused to the asphalt layer. The superhydrophobic asphalt has a water contact angle of 145 to 170°, above the classification threshold for superhydrophobicity. The method of preparing the superhydrophobic asphalt involves distributing polypropylene granules over the surface of a polymer modified asphalt and curing below the melting temperature of the polypropylene. The asphalt may find use in waterproofing applications such as roofing.

STATEMENT OF PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in the article “Waterresistance and characteristics of asphalt surfaces treated withmicronized-recycled-polypropylene waste: Super-hydrophobicity” publishedin Construction and Building Materials, 2021, Vol. 285, Page 122870,available on Mar. 11, 2021, which is incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a method of preparing a superhydrophicasphalt, a superhydrophic asphalt surface, and a superhydrophobicasphalt produced by the method.

Discussion of the Background

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Asphalt binder is one of the oldest known civil engineering materialsemployed for roofing, damp proofing, and waterproofing applications.This is mainly because asphalt binder is water-resistant, a propertythat makes it suitable for such applications. However, studies haveshown that conventional and modified asphalt binders are onlyhydrophobic, not superhydrophobic (SH) [M.A. Dalhat, and A.Y. Adesina,Constr. Build. Mater. 240 (2020), incorporated by reference herein inits entirety]. Hydrophobic surfaces are characterized by Water ContactAngle (WCA) value that is greater than 90° and less than 145°, whileSuperhydrophobic surfaces exhibit WCA greater than 145° [K.Y. Law, J.Phys. Chem. Lett. 5 (4) (2014) 686-688]. Superhydrophobic surfacespossess exceptional water resistance properties, such that they arenon-wetting due to their high WCA [J. Jeevahan, et. al., J. CoatingsTechnol. Res. 15 (2) (2018) 231-250]. Superhydrophobic surfaces holdseveral advantages over hydrophobic surfaces for engineeringapplications such as anti-icing, dust/mud self-cleaning, and corrosionresistance [X. Yan, et. al., in: 2012 Int. Conf. High Volt. Eng. Appl.,2012, pp. 282-285; C. Peng, et. al., Constr. Build. Mater. 264 (2020)120702; C. Yu, et. al., Chem. Eng. Res. Des. 155 (2020) 48-65; M. Cui,et. al., Surf. Coatings Technol. 347 (2018) 38-45]. Snow build-up onroof tops is still an issue that results in accidents during manualcleaning [P.O. Bylund, et. al., Int. J. Inj. Contr. Saf. Promot. 23 (1)(2016) 105-109]. Snow build-up can lead to roof collapse due to overloadand high energy requirements for indoor heating [A.C. Altunişik, et.al., Eng. Fail. Anal. 72 (2017) 67-78; O. Michael and W. Jennifer,Snow-Related Roof Collapse during the Winter of 2010-2011: implicationsfor Building Codes, 2014; and M. Zhao, et. al., Build. Environ. 87(2015) 82-91]. Accumulation of dust on asphalt roofs leads to soilingwhich in turn leads to fungal growth and degradation in high rainfallareas [P. Berdahl, et. al., Constr. Build. Mater. 22 (4) (2008)423-433]. All of these aforementioned problems can be minimized oreliminated if roof surfaces can be made superhydrophobic.

Recycling is still considered among the key strategies of managing theplastic waste crisis of this era [R.C. Thompson, et. al., Philos. Trans.R. Soc. B Biol. Sci. 364 (1526) (2009) 2153-2166]. Studies have shownthat unless a high plastic waste recycling rate and similar stringentwaste management targets are achieved, the current environmental issuesassociated with plastic waste will worsen past the middle of the 21thcentury [L. Lebreton and A. Andrady, Palgrave Commun. 5 (2019) 6]. Onefacet of improving plastic recycling is to identify and create moreproducts and uses for recycled plastic materials. The use of recycledpolypropylene for preparing superhydrophobic materials may provide animportant environmental benefit.

A wide variety of different asphalt formulations and asphalt additiveshave been investigated to determine and improve hydrophobicity. Study ofthe moisture susceptibility of asphalt mixtures reveals that the WCA of60-70 penetration grade binder and its modified version containing waxand nano-materials lies in the range of 102°- 105° [M. Arabani, et. al.,J. Mater. Civ. Eng. 24 (7) (2012) 889-897]. In a study of asphalt bindersurface free energy, a WCA of 60-100 penetration grade asphalt bindersfrom six different sources was evaluated [A. Bahramian, Evaluatingsurface energy components of asphalt binders using Wilhelmy plate andsessile drop techniques, Royal Institute of Technology (KTH) (2012)].The estimated WCA of the various asphalt binders revealed values thatranged between 100° and 104°. Similar research on the water resistanceof 10 different asphalt binders also showed that five of the 70# asphaltbinders have WCA of 95° ± 7°, while styrene-butadienestyrene (SBS)modified asphalt binders and those with performance grade (PG) 76 showedWCA of 99° ± 5° [F. Zhang, et. al., Constr. Build. Mater. 176 (2018)422-431]. The effect of c-(methacryloyloxy)-propyl-trimethoxy-silanecoupling agent on the wettability of asphalt binder was also assessed[X. Liang, et. al., Appl. Mech. Mater. 105-107 (2012) 1773-1778].Modification of the asphalt binder with up to 1% of the coupling agentraises its WCA from 97° to 102°. In another study of moisturesusceptibility of modified asphalt binder using surface free energy, WCAof different binders obtained by modifying a PG 64-22 asphalt withnano-clay, devulcanized rubber, fly-ash, and SBS polymer was evaluated[J. Hu, et. al., Constr. Build. Mater. 256 (2020) 119429]. Maximumaverage WCAs of 89.8°, 88.6°, 90.6°, & 100.0° were recorded for 4% SBS,2% nanoclay, 2% fly-ash, and 3.5% devulcanized-rubber modified asphaltbinders respectively. However, in another study, a PG 64-16 asphaltbinder upgraded to PG 70 and PG 76 using 1% and 4% SBS modificationshowed higher WCA of 106.3° and 109.9° respectively [M.A. Dalhat, andA.Y. Adesina, J. Mater. Civ. Eng. 31 (2019) 4019229, incorporated byreference herein in its entirety]. Modifying the asphalt binder with upto 20% polyurethane was not found to improve the WCA of the controlasphalt binder before (100.85°) and after (106.32°) aging by anysignificant amount [C. Peng, et. al., Constr. Build. Mater. 247 (2020)118547]. An earlier study showed that although modifying the asphaltbinder with ground tire rubber (GTR) increases the asphalt cohesiveenergy, mixing the asphalt with 20% of GTR causes a decline in WCA ofthe binder from 98° to 83°, thereby leading to higherwater-wetting-susceptibility of the asphalt [Z. Hossain, et. al.,Constr. Build. Mater. 95 (2015) 45-53]. Based on existing literature,regular asphalt binders and those modified using conventional asphaltmodification showed WCAs below 110°. These WCA values are significantlyless than the minimum WCA limit of 145° for superhydrophobic surfaces.These previous research findings call for a different and or alternativeapproach towards improvement of asphalt binder WCA and moistureresistance.

Until recently, superhydrophobic properties were only reported onmaterials other than asphalt binder. Superhydrophobicpolymethylmethacrylate (PMMA) surface was previously achieved by 12 hhard pressing, 30 min washing, 1 h baking at 50° C., and finally coatingthe PMMA surface with polydimethylsiloxane (PDMS) [Yung-Tsan Lin andJung-Hua Chou, J. Mater. Sci. 50 (20) (2015) 6624-6630]. PMMA surfaceswith 152.6° ± 1° WCA measurements were reported. Other studies reportedachieving superhydrophobic properties using chemical functionalization.An example is silica-based suspension spray which was activated byperfluoro-decyl-tri-ethoxy-silane to form superhydrophobic surface [Q.Shang, et. al., J. Coat. Technol. Res. 11 (4) (2014) 509-515]. A recentstudy explored the potential of using 8 hydrophobic chemical treatmentsto reduce ice adhesion on asphalt concrete [M. Zakerzadeh, et. al.,Constr. Build. Mater. 180 (2018) 285-290]. Of the 8 chemicals studied,only one (2,2,3,3,4,4,5,5-octafluoropentyl methacrylate) resulted inasphalt concrete surface with WCA above superhydrophobic limit (156°),after 24 h of curing. The other treated asphalt concrete surfaces showedWCA in the range of 130.2° ± 7°. In a non-conventional asphaltmodification, superhydrophobic asphalt surface was also derived bythermally fusing micronized waste tire rubber of variables sizes on tothe asphalt surface [M.A. Dalhat, and A.Y. Adesina, J. Mater. Civ. Eng.31 (2019) 4019229]. A WCA of up to 156.2° was observed for thermalcuring duration of 25 min. Another similar study used thermal treatmentand micronized recycled polyethylene to attain SH asphalt surface withWCA of up to 155.9° [M.A. Dalhat, and A.Y. Adesina, Constr. Build.Mater. 240 (2020)]. To date no superhydrophobic asphalts based onrecycled polypropylene have been reported, specifically recycledpolypropylene (RPP) waste.

In view of the foregoing, it is an objective of the present disclosureto provide a method of forming a superhydrophobic asphalt andsuperhydrophobic asphalt surface using polypropylene and asuperhydrophobic asphalt comprising an asphalt layer and a polypropylenelayer.

SUMMARY OF THE INVENTION

The present disclosure relates to a method of forming a superhydrophobicasphalt, the method comprising applying a layer of polypropylenegranules to a surface of a polymer modified asphalt to form an uncuredcoated asphalt; and curing the uncured coated asphalt at 75 to 150° C.to form the superhydrophobic asphalt, wherein the superhydrophobicasphalt comprises a polypropylene layer disposed upon an asphalt layer;the superhydrophobic asphalt has a water contact angle of 145 to 170°;and the polypropylene granules are substantially free of fluoropolymersand have a maximum particle size of 250 µm.

In some embodiments, the polymer modified asphalt is an elastomer-typepolymer modified asphalt.

In some embodiments, the elastomer-type polymer modified asphalt isstyrene-butadiene styrene (SBS)-modified asphalt.

In some embodiments, the styrene-butadiene-styrene is a radialstyrene-butadiene-styrene and is present in an amount of 0.5 to 10 wt%based on a total weight of the styrene-butadiene styrene (SBS)-modifiedasphalt.

In some embodiments, the method further comprises mixing anon-polymer-modified asphalt having a performance grade of 64-16 with0.5 to 10 wt% of an elastomer type polymer at 150 to 200° C. to form theelastomer-type polymer modified asphalt.

In some embodiments, the polymer modified asphalt has a softening pointof 80 to 95° C., a viscosity at 135° C. of 1575 to 1650 cP, a ductilityat 25° C. of 11.5 to 17.5 cm, a flash point of 300 to 360° C., and aperformance grade of 76-10.

In some embodiments, the polypropylene granules are present in theuncured coated asphalt in an amount of 185 to 275 g polypropylenegranules per m² of surface of the asphalt.

In some embodiments, the polypropylene granules have a minimum particlesize of 100 µm.

In some embodiments, the curing is performed for 15 to 90 minutes.

In some embodiments, the polypropylene layer is present in an amount of50 to 125 g per m² of polymer modified asphalt layer.

In some embodiments, the superhydrophobic asphalt has a work of adhesionof 1 to 15 mN/m.

In some embodiments, the polypropylene layer has a R_(a) surfaceroughness of 10 to 50 µm.

The present disclosure also relates to a superhydrophobic asphalt,comprising an asphalt layer comprising a polymer modified asphalt; and apolypropylene layer comprising polypropylene granules thermally fusedonto the asphalt layer, wherein the superhydrophobic asphalt has a watercontact angle of 145 to 170 ° and a R_(a) surface roughness of 10 to 50µm; and the polymer granules are substantially free of fluoropolymersand have a maximum particle size of 177 µm.

In some embodiments, the polymer modified asphalt has a softening pointof 80 to 95° C., a viscosity at 135° C. of 1575 to 1650 cP, a ductilityat 25° C. of 11.5 to 17.5 cm, a flash point of 300 to 360° C., and aperformance grade of 76-10.

In some embodiments, the polymer modified asphalt is an elastomer-typepolymer modified asphalt.

In some embodiments, the elastomer-type modified asphalt isstyrene-butadiene styrene (SBS)-modified asphalt.

In some embodiments, the styrene-butadiene-styrene is a radialstyrene-butadiene-styrene and is present in an amount of 0.5 to 10 wt%based on a total weight of the styrene-butadiene styrene (SBS)-modifiedasphalt.

In some embodiments, the polypropylene layer is present in an amount of50 to 125 g per m² of polymer modified asphalt layer.

In some embodiments, the superhydrophobic asphalt is substantially freeof silanes and/or siloxanes.

In some embodiments, the superhydrophobic asphalt has a work of adhesionof 1 to 15 mN/m.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a summary of an exemplary superhydrophobic asphaltpreparation process according to an embodiment of the present invention;

FIG. 2 is an image of milled RPP waste;

FIGS. 3A-3B are SEM images of RPP powders, where FIG. 3A is mesh #80 RPPand FIG. 3B is mesh #100 RPP;

FIG. 4 is an SEM image of the SBS-modified asphalt substrate;

FIGS. 5A-5B are images of the water contact angle measurements formaterials used in the method of present invention, where FIG. 5A is theuntreated modified asphalt substrate and FIG. 5B is a polypropylenesheet;

FIG. 6 is a plot of the Differential Scanning Calorimetry (DSC) analysisof RPP;

FIG. 7 is a plot of the surface roughness results of the RPP-treatedasphalt surfaces;

FIGS. 8A-8F are 3D plots of the surface profile of asphalt substratetreated with RPP-mesh #80 cured for 25 min (FIG. 8A), 40 min (FIG. 8B),55 min (FIG. 8C), and RPP-mesh #100 cured for 25 min (FIG. 8D), 40 min(FIG. 8E), and 55 min (FIG. 8F);

FIG. 9 is a plot of RPP mass accumulation curves vs. curing time;

FIG. 10 is a plot of water contact angle measurement results of theRPP-treated asphalt surfaces;

FIGS. 11A-11F are images of the water contact angle measurements ofasphalt substrate treated with RPP-mesh #80 cured for 25 min (FIG. 11A),40 min (FIG. 11B), 55 min (FIG. 11C), and RPP-mesh #100 cured for 25 min(FIG. 11D), 40 min (FIG. 11E), and 55 min (FIG. 11F);

FIG. 12 is a plot of water contact angle of various RPP-treated surfacesbefore and after 12 month exposure; and

FIGS. 13A-13D are SEM images of RPP-treated asphalt surfaces where FIG.13A is a low magnification image of a surface prepared with mesh #80 anda 55 minute curing time, FIG. 13B is a high magnification image of asurface prepared with mesh #80 and a 55 minute curing time, FIG. 13C isa low magnification image of a surface prepared with mesh #100 and a 55minute curing time, FIG. 13D is a high magnification image of a surfaceprepared with mesh #100 and a 55 minute curing time.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

As used herein the words “a” and “an” and the like carry the meaning of“one or more.”

As used herein, the terms “optional” or “optionally” means that thesubsequently described event(s) can or cannot occur or the subsequentlydescribed component(s) may or may not be present (e.g., 0 wt.%).

The phrase “substantially free”, unless otherwise specified, describes aparticular component being present in an amount of less than about 1wt%, preferably less than about 0.5 wt%, more preferably less than about0.1 wt%, even more preferably less than about 0.05 wt%, even morepreferably less than about 0.01 wt%, even more preferably less thanabout 0.001 wt%, yet even more preferably 0 wt%, relative to a totalweight of the composition being discussed.

Asphalt is a colloidal system similar to petroleum, but with lightermolecules removed. Asphalt can be fractionated into 4 major components:saturates, aromatics, resins and asphaltenes. The fractionated part ofsaturates and aromatics is considered as gas oil. Polarity of these fourfractions can be arranged as: saturates<aromatics<resin<asphaltenes.

Asphalt grading is given in accordance with accepted standards in theindustry as discussed in the booklet SUPERPAVE Series No. 1 (SP-1), 1997printing, published by the Asphalt Institute (Research Park Drive, P.O.Box 14052, Lexington, Ky. 40512-4052), as well as AASHTO ProvisionalStandard MP-1, each of which is incorporated herein by reference in itsentirety. Asphalt compositions are frequently given performance grades,for example, PG 64-22. The first number, 64, represents the average7-day maximum pavement design temperature in °C. The second number, -22,represents the minimum pavement design temperature in °C. Otherrequirements of each grade are as required by AASHTO ProvisionalStandard MP-1. For example, the maximum value for the PAV-DSR test (°C.)for PG 64-22 is 25° C.

According to a first aspect, the present disclosure relates to a methodof forming a superhydrophobic asphalt, the method comprising applying alayer of polypropylene granules to a surface of a polymer modifiedasphalt to form an uncured coated asphalt, and curing the uncured coatedasphalt at 75 to 150° C. to form the superhydrophobic asphalt.

Asphalts are commonly modified with non-bituminous additives. Suchadditives may serve to change the physical or chemical properties of theasphalt, such as the softening point, stiffness, viscosity, ductility,cracking resistance, embrittlement resistance, oxidation resistance,rate of volatiles loss, elastic recovery, water contact angle, work ofadhesion, performance grade, and/or combination thereof. Examples ofnon-bituminous additives include, but are not limited to antioxidants,anti-stripping agents, stiffening agents, rejeuvenating agents,softening agents, and polymer additives.

Polymer additives typically refer to additives used for any suitablereason such as those outlined above which is polymeric in nature.Polymer additives used to make polymer modified asphalt are typicallydivided into two classes: plastomers and elastomers. Plastomers arepolymers which display a combination of both plasticity and elasticity.In the context of asphalt additives, plastomers typically increase thestiffness and high temperature performance of asphalts, but may causeembrittlement, decreased low temperature performance, or loss of elasticrecovery. Examples of plastomers include, but are not limited topolyethylene, polypropylene, ethylene-vinyl acetate (EVA),ethylene-butyl acetate (EBA), polyvinyl chloride (PVC), and polyethyleneterephthalate (PET). Elastomers, in contract, are polymers which displayelasticity. In the context of asphalt additives, elastomers typicallyincrease the low temperature performance and elastic recovery ofasphalts, but may be associated with decreased stiffness. Examples ofelastomers include, but are not limited to styrene-butadiene rubber(SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene, andcrumb rubber. Asphalts which contain polymer additives are typicallyreferred to as polymer modified asphalts. In the context of the presentdisclosure, a polymer modified asphalt which contains a plastomer may bereferred to as a “plastomer-type polymer modified asphalt”, a polymermodified asphalt which contains an elastomer may be referred to as a“elastomer-type polymer modified asphalt”, and a polymer modifiedasphalt which contains both a plastomer and an elastomer may be referredto as a “combination-type polymer modified asphalt”.

Oxidation is a primary cause of long-term aging in asphalts andasphalt-containing materials. In this context, oxidation is theirreversible chemical reaction between oxygen molecules and thecomponent species of bulk asphalt resulting in significant alterationsto the desired physical and/or mechanical properties of asphalt.Oxidative aging of asphalt is believed to be caused by the generation ofoxygen-containing polar chemical functionalities on asphalt molecules,which in turn can cause agglomeration among molecules due to increasedintermolecular interactions such as hydrogen bonding, van der Waalsforce, and Coulomb force. Oxidation is typically associated withcompositional changes in the asphalt that result in decreased aromaticfractions and increased asphaltenes fractions. As the asphalt oxidizes,it stiffens and can eventually crack. Antioxidants are commonly added toprevent, slow the rate of, reduce the amount of, or otherwise mitigateoxidation of asphalts. Examples of antioxidants used as additives forasphalt include, but are not limited to aldehydes such as furfural,formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, acrolein,cotonaldehye, tiglaldehyde, benzaldehyde, salicylaldehye, furfuralalcohol, paraformaldehyde, cinnamaldehyde; thioesters such as dilaurylthiodipropionate (DLTDP), distearylthiodipropionate, and dimethyl3,3'-thiodipropionate; lignin; vitamin E; Irganox® 1010 (available fromBASF); and tetrakis(2,4-di-tert-butylphenyl)[1,1'-biphenyl]-4,4'-diylbis(phosphonite) (sold as Irgafos P-EPQ ® byBASF).

A popular approach for mitigating the susceptibility of asphalt mixes tomoisture damage (typically referred to as “stripping”) is addinganti-stripping agents, particularly liquid anti-stripping agents (LAS),to asphalt. Anti-stripping agents are frequently surface active agentsthat can be added to asphalt, emulsion, and cutbacks. Generally,anti-stripping agents reduce the surface tension and increase thewettability of aggregates or surface layers, which produces betteradhesion between the asphalt and the aggregate or surface layer. Whilethe chemical composition of most commercially produced anti-strippingagents is proprietary, most anti-stripping agents contain amines.Examples of anti-stripping agents include amidoamines, imidazolines,polyamines, hydrated lime, amine-containing organometallics, and aminoacids.

Stiffening agents are additives which increase the stiffness of anasphalt. Typically, stiffening agents are used in conjunction with otheradditives which may decrease the stiffness of the asphalt. In suchsituations, the stiffening agents are used to compensate for thisdecrease. Examples of stiffening agents include, but are not limited topolyphosphoric acid and gilsonite. Polyphosphoric acid in particular iscommonly used in polymer modified asphalts, where it may serve tocrosslink the polymer additive. Gilsonite (also known as asphaltite,uintahite, or asphaltum) is a naturally occurring soluble solidhydrocarbon mixture with a relatively high melting temperature.Gilsonite itself is rarely used as the major component in asphalts dueto factors such as high melting temperature causing difficulty in mixingand application and poor low temperature performance, particularlyembrittlement.

Rejuvenating agents and softening agents are additives typically used inrecycled asphalts. Rejuvenating agents typically refer to additiveswhich are intended to restore the rheological and chemical properties ofan aged asphalt. Softening agents typically refers to additives whichlower the viscosity of an aged asphalt. The aged asphalt may undergoprocesses such as volatiles loss or oxidation which change the chemicalcomposition of the asphalt. A common strategy for mitigating suchchanges involves adding in components similar to the volatiles lost(softening agents) or components oxidized (rejuvenating agents). Forthis reason, rejuvenating agents and softening agents typically compriseoils comprising components such as saturated aliphatic hydrocarbons,monoaromatic hydrocarbons, diaromatic hydrocarbons, polyaromatichydrocarbons, polar compounds and basic, pyridene-soluble compounds.

For additional information and examples of asphalt additives, see Porto,et. al. [Porto, M., et. al., Applied Sciences, 2019, 742, incorporatedherein by reference in its entirety].

In the context of the present disclosure, the polymer modified asphaltmay be any suitable polymer modified asphalt known to one of ordinaryskill in the art. Such a polymer modified asphalt may comprise one ormore other suitable additives such as those described above. The polymermodified asphalt may be a plastomer-type polymer modified asphalt, anelastomer-type polymer modified asphalt, or a combination-type polymermodified asphalt. In preferred embodiments, the polymer modified asphaltis an elastomer-type polymer modified asphalt. In some embodiments, theelastomer-type polymer modified asphalt comprises the elastomerstyrene-butadiene-styrene (SBS). In preferred embodiments, theelastomer-type polymer modified asphalt is styrene-butadiene styrene(SBS)-modified asphalt. Such an asphalt is preferably devoid ofplastomers and of non-SBS elastomers.

Styrene-butadiene-styrene (SBS) is a block copolymer of styrene andbutadiene. SBS comprises at least one block of poly(butadiene) and atleast two blocks of polystyrene. SBS is typically divided into two typesbased upon the arrangement of the poly(butadiene) block(s) and thepolystyrene blocks. Linear SBS comprises a linear arrangement ofalternating poly(butadiene) and polystyrene blocks, with eachpoly(butadiene) block having a polystyrene block attached to both ends.In this way, a single poly(butadiene) block is flanked by polystyreneblocks, with a polystyrene block forming each terminus of the lineararrangement. A common arrangement of linear SBS is a single polystyreneblock, a single poly(butadiene) block, and a single polystyrene block.Examples of linear SBS elastomers, particularly those useful as asphaltadditives include, but are not limited to Pavprene ® 501, Pavprene ®501P, Kraton ® D1192, Kraton ® D1101, and LG™ SBS LG-501. Radial SBS, incontrast, comprises a branched poly(butadiene) block which has more thantwo polymer chain ends, each of which is connected to a polystyreneblock. This give the radial SBS a star-shaped profile in which a centralpoly(butadiene) block is connected to multiple projecting polystyreneblocks. Examples of radial SBS elastomers, particularly those useful asasphalt additives include, but are not limited to Pavprene ® 511K,Pavprene ® 511P, Pavprene ® 511C, Kraton ® D1184, Kraton ® D1191, andLG™ SBS LG-411. In some embodiments, the SBS-modified asphalt comprisesradial SBS. In some embodiments, the SBS-modified asphalt issubstantially free of linear SBS.

In some embodiments, the radial SBS is present in an amount of 0.5 to 10wt%, preferably 0.75 to 9.5 wt%, preferably 1 to 9.0 wt%, preferably1.25 to 8.5 wt%, preferably 1.5 to 8.0 wt%, preferably 1.75 to 7.5 wt%,preferably 2.0 to 7.0 wt%, preferably 2.25 to 6.5 wt%, preferably 2.5 to6.0 wt%, preferably 2.75 to 5.5 wt%, preferably 3.0 to 5.0 wt%,preferably 3.25 to 4.75 wt%, preferably 3.5 to 4.5 wt%, preferably 3.75to 4.25 wt%, preferably 3.9 to 4.1 wt%, preferably 4 wt% based on atotal weight of the styrene-butadiene styrene (SBS)-modified asphalt.

An asphalt may be characterized by a quantity of asphaltenes, saturates,aromatics, and resins which may be fractionated. This composition istypically referred to as the SARA composition. Oils from differentregions have different compositions based on saturates, aromatics,resins, and asphaltenes, thus the asphalts extracted from these sourcesalso typically have a different composition. For example, from westernCanadian oils saturates may be from 8 to 17 wt% relative to the totaloil, aromatics may be from 36 to 44 wt% relative to the total oil,resins may be from 18 to 27 wt% relative to the total oil, asphaltenesmay be from 15 to 20 wt% relative to the total oil; from Arabian oilssaturates may be from 22 to 25 wt% relative to the total oil, aromaticsmay be from 26 to 50 wt% relative to the total oil, resin may be 10 to18 wt% relative to the total oil, and asphaltenes may be 30 to 36 wt%relative to the total oil; and from Sumatran oils, saturates from 44 to46 wt% relative to the total oil, aromatics may be from 30 to 33 wt%relative to the total oil, resins may be from 15 to 17 wt% relative tothe total oil, asphaltenes may be from 7 to 10 wt% relative to the totaloil. These quantities of asphaltenes, saturates, aromatics, and resinstypically change from crude oil to asphalt as a result of the refiningprocess. Further, these quantities may be changed by the addition ofasphalt additives described above. In some embodiments, the polymermodified asphalt has a SARA composition comprising 25.0 to 30.0 wt%,preferably 25.5 to 29.5 wt%, preferably 26.0 to 29.0 preferably 26.25 to28.50 preferably 26.5 to 28.25 wt%, preferably 26.75 to 28.0 wt%,preferably 27.0 to 27.75 wt%, preferably 27.25 to 27.5 wt%, preferably27.3 wt% saturate. In some embodiments, the polymer modified asphalt hasa SARA composition comprising 22.0 to 27.5 wt%, preferably 22.5 to 27.0wt% preferably 23.0 to 26.5 wt%, preferably 23.5 to 26 wt%, preferably23.75 to 25.75 wt%, preferably 24.0 to 25.5 wt%, preferably 24.25 to25.25 wt%, preferably 24.5 to 25 wt%, preferably 24.6 to 24.85 wt%,preferably 24.7 to 24.8 wt% aromatics. In some embodiments, the polymermodified asphalt has a SARA composition comprising 17.0 to 21.5 wt%,preferably 18.5 to 21.25 wt%, preferably 18.0 to 21.0 wt%, preferably18.25 to 20.75 wt%, preferably 18.5 to 20.5 wt% preferably 18.75 to20.25 wt%, preferably 19.0 to 20.0 wt%, preferably 19.1 to 19.4 wt%,preferably 19.2 to 19.3 wt% resins. In some embodiments, the polymermodified asphalt has a SARA composition comprising 21 to 36 wt%,preferably 22.0 to 35.0 wt%, preferably 23.0 to 34.5 wt%, preferably23.5 to 34.0 wt%, preferably 24 to 33.5 wt%, preferably 24.5 to 33.0wt%, preferably 25 to 32.5 wt%, preferably 25.5 to 32.0 wt% preferably26.0 to 31.5 wt%, preferably 26.5 to 31 wt%, preferably 26.75 to 30.75wt%, preferably 27.0 to 30.5 wt%, preferably 27.25 to 30.25 wt%,preferably 27.5 to 30 wt%, preferably 27.75 to 29.75 wt%, preferably28.0 to 29.5 wt% preferably 28.25 to 29.25 wt%, preferably 28.5 to 29.0wt%, preferably 28.6 to 28.9 wt%, preferably 28.7 to 28.8 wt%asphaltene. Typically, the SARA composition of an asphalt is determinedaccording to ASTM:D4124 [ASTM:D4124-09, Standard Test Method forSeparation of Asphalt into Four Fractions, ASTM Int. West Conshohocken,PA. (2018). 10.1520/D4124-09R18].

In some embodiments, the elastomer-type polymer modified asphalt isprepared by mixing a non-polymer-modified asphalt having a performancegrade of 64-16 with 0.5 to 10 wt%, preferably 0.75 to 9.5 wt%,preferably 1 to 9.0 wt%, preferably 1.25 to 8.5 wt%, preferably 1.5 to8.0 wt%, preferably 1.75 to 7.5 wt%, preferably 2.0 to 7.0 wt%,preferably 2.25 to 6.5 wt%, preferably 2.5 to 6.0 wt%, preferably 2.75to 5.5 wt%, preferably 3.0 to 5.0 wt%, preferably 3.25 to 4.75 wt%,preferably 3.5 to 4.5 wt%, preferably 3.75 to 4.25 wt%, preferably 3.9to 4.1 wt%, preferably 4 wt% of an elastomer type polymer at 150 to 200°C., preferably 160 to 195° C., preferably 170 to 190° C., preferably 175to 185° C., preferably 180° C. Preferably, the elastomer type polymer isSBS as described above. In preferred embodiments, the elastomer typepolymer is a radial SBS as described above. The mixing may be performedusing any suitable material or method known to one of ordinary skill inthe art. In some embodiments, the mixing is performed at 1000 to 5000rpm, preferably 1500 to 4500 rpm, preferably 2000 to 4000 rpm,preferably 2500 to 3500 rpm, preferably 3000 rpm. In some embodiments,the mixing is performed for 15 to 120 minutes, preferably 30 to 90minutes, preferably 45 to 75 minutes, preferably 60 minutes.

In some embodiments, the polymer modified asphalt has a softening pointof 80 to 95° C., preferably 81 to 92° C., preferably 82 to 90 C,preferably 83 to 89° C., preferably 84 to 88° C., preferably 85 to 87°C., preferably 86° C. The softening point may be measured by anysuitable technique known to one of ordinary skill in the art. Onestandard method used is the ring and ball method for softening pointtest [ASTM:D36, Standard Test Method for Softening Point of Bitumen(Ring-and-Ball Apparatus), ASTM Int. West Conshohocken, PA. (2014)]. Insome embodiments, the polymer modified asphalt has a viscosity at 135°C. of 1575 to 1650 cP, preferably 1580 to 1645 cP, preferably 1585 to1640 cP, preferably 1590 to 1635 cP, preferably 1595 to 1630 cP,preferably 1600 to 1625 cP, preferably 1605 to 1620 cP, preferably 1610to 1615 cP. The viscosity may be measured by any suitable techniqueknown to one of ordinary skill in the art. One standard method uses therotational viscometer and is outlined in ASTM:D4402 [ASTM:D4402,Standard Test Method for Viscosity Determination of Asphalt at ElevatedTemperatures Using a Rotational Viscometer., ASTM Int. WestConshohocken, PA. (2015)]. In some embodiments, the polymer modifiedasphalt has a ductility at 25° C. of 11.5 to 17.5 cm, preferably 11.75to 17.25 cm, preferably 12 to 17 cm, preferably 12.25 to 16.75 cm,preferably 12.5 to 16.5 cm, preferably 12.75 to 16.25 cm, preferably 13to 16 cm, preferably 13.25 to 15.75 cm, preferably 13.5 to 15.5 cm,preferably 13.75 to 15.25 cm, preferably 14 to 15 cm, preferably 14.25to 14.75 cm, preferably 14.5 cm. The ductility may be measured by anysuitable technique known to one of ordinary skill in the art. Onestandard is outlined in ASTM D113 [ASTM:D113-17, Standard Test Methodfor Ductility of Asphalt Materials, ASTM Int. West Conshohocken, PA.(2017)]. In some embodiments, the polymer modified asphalt has a flashpoint of 300 to 360° C., preferably 305 to 355° C., preferably 310 to350° C., preferably 315 to 345° C., preferably 320 to 340° C.,preferably 325 to 335° C., preferably 330° C. The flash point may bemeasured by any suitable technique known to one of ordinary skill in theart. One standard method used is the Cleveland open-cup test[ASTM:D92-18, Standard Test Method for Flash and Fire Points byCleveland Open Cup Tester., ASTM Int. West Conshohocken, PA. (2018)]. Insome embodiments, the polymer modified asphalt has a performance gradeof 76-10.

The polypropylene granules may be granules of any suitable polypropyleneknown to one of ordinary skill in the art. The polypropylene may becharacterized by mechanical properties, thermal properties, chemicalproperties, or a combination of these. In some embodiments, thepolypropylene has a bulk density of 0.850 to 0.950 g/cm³, preferably0.860 to 0.945 g/cm³, preferably 0.875 to 0.940 g/cm³, preferably 0.880to 0.935 g/cm³, preferably 0.885 to 0.930 g/cm³, preferably 0.890 to0.925 g/cm³, preferably 0.895 to 0.920 g/cm³. In some embodiments thepolypropylene has a melting point of 130 to 171° C., preferably 140 to168° C., preferably 150 to 166° C., preferably 160 to 165° C.,preferably 161 to 163° C., preferably 162° C. The polypropylene may betotally crystalline, totally amorphous, be of intermediatecrystallinity. The polypropylene may be atactic, syndiotactic,isotactic, or a combination thereof. While the polypropylene may containappropriate additives known to one of ordinary skill in the art, such asdyes, plasticizers, crosslinkers, and the like, the polypropylene shouldbe substantially free of fluoropolymers. Such fluoropolymers aresometimes integrated into the bulk of a polypropylene sample and/ordisposed on a surface of a polypropylene sample. In some embodiments,the polypropylene is substantially free of polyethylene.

Preferably, the polypropylene is used in the form of granules. Thesegranules may be formed by any suitable technique or combination oftechniques known to one of ordinary skill in the art. For example, thepolypropylene granules may be formed using a technique which involvesthe solidification of a liquid polypropylene such as extrusion,thermoforming, molding, blowing, and rotational forming. Alternatively,the polypropylene granules may be formed by reducing a largerpolypropylene sample to smaller particles. Such a reduction to smallerparticles may be performed by any suitable technique or with anysuitable equipment known to one of ordinary skill in the art. Examplesof such techniques include, but are not limited to, milling, grinding,ball milling, chopping, pulverizing, crushing, pounding, mincing,shredding, smashing, and fragmenting. In some embodiments, the millingmay take place using a mill, ball mill, rod mill, autogenous mill,cutting mill, semi-autogenous grinding mill, pebble mill, buhrstonemill, burr mill, tower mill, vertical shaft impactor mill, a low energymilling machine, grinder, pulverizer, mortar and pestle, blender,crusher, or other implement used to reduce a material to smallparticles. Preferably, the polypropylene granules are separated by sizefollowing the reduction to smaller particles. Such separation by sizemay be performed using any suitable technique or with any suitableequipment known to one of ordinary skill in the art. In preferredembodiments, the granules are sieved. The granules which pass through asieve may be defined by a maximum size capable of passing through thesieve, the maximum size defined by a sieve spacing. The granules whichare retained by a sieve may be defined by a minimum size which isincapable of passing through the sieve, the minimum size defined by thesieve spacing.

The polypropylene granules used in the method should have a maximumparticle size of 250 µm, preferably 245 µm, preferably 240 µm,preferably 235 µm, preferably 230 µm, preferably 225 µm, preferably 220µm, preferably 215 µm, preferably 210 µm, preferably 205 µm, preferably200 µm, preferably 195 µm, preferably 190 µm, preferably 185 µm,preferably 180 µm, preferably 177 µm.Preferably, this maximum size isdetermined by passing the granules through a sieve which is designed toretain particles having a size larger than the maximum size. Suchretained particles are thus separated from the particles which passthrough the sieve, said particles which pass through then being used asthe granules. In some embodiments, the polypropylene granules have aminimum size of 100 µm, preferably 105 µm, preferably 110 µm, preferably115 µm, preferably 120 µm, preferably 125 µm, preferably 130 µm,preferably 135 µm, preferably 140 µm, preferably 145 µm, preferably 149µm.Preferably, this minimum size is determined by passing the granulesthrough a sieve which is designed to retain particles having a sizeequal to or larger than the minimum size. These retained particles arethen used as the granules.

In general, the polypropylene granules may be any suitable shape knownto one of ordinary skill in the art. Examples of such suitable shapesinclude, but are not limited to spheres, cylinders, boxes, spikes,flakes, plates, ellipsoids, stars, ribbons, discs, rods, prisms, cones,platelets, and sheets.

The polypropylene granules may be applied to the polymer modifiedasphalt using any suitable technique known to one of ordinary skill inthe art. Preferably, the polypropylene granules are applied in such amanner so as to uniformly cover an entirety of the surface of thepolymer modified asphalt. In some embodiments, the polypropylenegranules are present in the uncured coated asphalt in an amount of 185to 275, preferably 190 to 270 g, preferably 195 to 265 g, preferably 200to 260 g, preferably 205 to 255 g, preferably 210 to 250 g, preferably215 to 245 g polypropylene granules per m² of surface of the polymermodified asphalt.

The curing is performed at 75 to 150° C., preferably 80 to 140° C.,preferably 85 to 130° C., preferably 90 to 120° C., preferably 95 to110° C., preferably 100° C. The curing is preferably performed below themelting temperature of the polypropylene granules. Such melting may bedisadvantageous to achieving the desired superhydrophobic properties. Insome embodiments, the curing is performed for 15 to 90 minutes,preferably 20 to 80 minutes, preferably 25 to 70 minutes, preferably 30to 65 minutes, preferably 35 to 60 minutes, preferably 40 to 55 minutes.

The superhydrophobic asphalt produced comprises a polypropylene layerdisposed upon an asphalt layer. The asphalt layer comprises the polymermodified asphalt as described above. The polypropylene layer comprisesthe polypropylene granules which are thermally fused to the asphaltlayer. The thermal fusing may involve softening or partial melting ofthe polylmer modified asphalt such that the polypropylene granulesbecome partially or totally embedded in the asphalt layer. In someembodiments, the polypropylene layer is present in an amount of 50 to125 g, preferably 55 to 115 g, preferably 60 to 110 g, preferably 65 to105 g, preferably 70 to 100 g, preferably 75 to 95 g, preferably 80 to90 g per m² of asphalt layer. Preferably, the polypropylene granulespresent in the polypropylene layer are substantially similar to thepolypropylene granules which were applied to form the uncured coatedasphalt. Such similarity may be in the particle size, particle shape, orboth. Similarity in the particle size may be such that the size of thepolypropylene granules present in the polypropylene layer (i.e. aftercuring) differs from the size of the polypropylene granules used to formthe uncured coated asphalt by no more than 25%, preferably no more than20%, preferably no more than 15%, preferably no more than 10%,preferably no more than 7.5%, preferably no more than 5%, preferably nomore than 2.5%. Such a size may be a mean size, a median size, a maximumsize, or a minimum size.

In some embodiments, the granules are embedded in the surface of thepolymer modified asphalt such that the granule comprises a protrusionportion and an embedded portion. The protrusion portion extends abovethe surface of the polymer modified asphalt in the immediate area of thegranule while the embedded portion is embedded within the polymermodified asphalt. The embedded portion may be surrounded by the polymermodified asphalt and extend below the surface of the polymer modifiedasphalt in the immediate area of the granule. In general, the protrusionportion may take on any suitable shape known to one of ordinary skill inthe art, such as those shapes described above. In some embodiments, theprotrusion portion may take on a shape which is defined by a contiguouspart of the shapes described above. Such contiguous parts may includeedges, vertices, and faces as appropriate. Examples of such shapesdefined by a contiguous part of the shapes described above include, butare not limited to a hemisphere formed from a sphere, a dome-shapeformed from a sphere or ellipsoid, a half disc from a disc, arectangular prism from a cube or rectangular prism, a pyramid having atriangular base from a cube or rectangular prism, a pyramid having asquare base from an octahedron, and an irregular shape formed from adifferent irregular shape. It should be noted that even in embodimentsin which the granules have a single shape, the shape of the protrusionportions formed from that shape may be different. In some embodiments,the protrusion portion has a protrusion portion size which is 5 to 50 %,preferably 6 to 45%, preferably 7 to 40%, preferably 8 to 37.5%,preferably 9 to 35%, preferably 10 to 32.5%, preferably 11 to 30%,preferably 12 to 27.5%, preferably 13 to 26%, preferably 13.5 to 25% ofa total size of the granule. In such embodiments, the remainder of thetotal size of the granule may comprise the embedded portion.

In some embodiments, the superhydrophobic asphalt is substantially freeof silanes and/or siloxanes. Such materials are commonly used toincrease hydrophobicity of various materials, including asphalts. Suchmaterials are frequently applied as surface treatments. The inclusion ofsuch materials as a surface layer or surface coating on thesuperhydrophobic asphalt is not envisioned in any embodiment. In someembodiments, the superhydrophobic asphalt is substantially free offluoropolymers. Fluoropolymers, particularly polytetrafluoroethylene(PTFE), are also commonly used to increase hydrophobicity of variousmaterials, including asphalts. The inclusion of such fluoropolymers,either as a component which is mixed into the polypropylene layer or asa surface layer or surface coating on the superhydrophobic asphalt isnot envisioned in any embodiment.

The superhydrophobic asphalt may be characterized by a standard measureof hydrophobicity known to one of ordinary skill in the art. Typically,hydrophobicity is measured by water contact angle. Standard procedureand specifications adopted for water contact angle measurements areprovided in ASTM D7334 [ASTM:D7334-08, Standard Practice for SurfaceWettability of Coating, Substrates and Pigments by Advancing ContactAngle Measurement, (2013), incorporated herein by reference in itsentirety]. In some embodiments, the superhydrophobic asphalt has a watercontact angle of 145 to 170°, preferably 147.5 to 167.5°, preferably 150to 165°, preferably 152.5 to 162.5°, preferably 153 to 160°. In someembodiments, the water contact angle is measured on a freshly-preparedsuperhydrophobic asphalt. Exposure to outdoor conditions, such assunlight, temperature fluctuations, precipitation, and seasonalvariation in the aforementioned parameters may cause a degradation orother structural change of the superhydrophobic asphalt which may beassociated with a lowering of the water contact angle. In someembodiments, the superhydrophobic asphalt has a post-exposure watercontact angle which is at least 85%, preferably at least 87.5%,preferably at least 90%, preferably at least 92.5%, preferably at least95%, preferably at least 97.5% of a pre-exposure water contact angleafter exposure to outdoor conditions for at least 6 months, preferablyat least 8 months, preferably at least 10 months, preferably at least 12months, preferably at least 14 months, preferably at least 16 months,preferably at least 18 months, preferably at least 20 months, preferablyat least 22 months, preferably at least 24 months. The superhydrophobicasphalt may be further characterized by the work of adhesion. The workof adhesion is a measure of the energy per unit area required toseparate un-absorbed liquid from a solid surface. Typically, hydrophobicand superhydrophobic surfaces have lower values for the work of adhesioncompared to hydrophilic surfaces. In some embodiments, thesuperhydrophobic asphalt has a work of adhesion of 1 to 15 mN/m,preferably 1.50 to 14 mN/m, preferably 2.00 to 13 mN/m, preferably 2.50to 12.5 mN/m, preferably 3.00 to 12.0 mN/m, preferably 3.5 to 11.75mN/m, preferably to 4.35 to 11.48 mN/m, preferably 6.50 to 9.60 mN/m.

The superhydrophobic asphalt may be characterized by a surface roughnessparameter which may be directly related to the superhydrophobicity asmeasured by, for example, water contact angle or work of adhesion asdescribed above. In some embodiments, the polypropylene layer has aR_(a) surface roughness of 10 to 50 µm, preferably 12.5 to 47.5 µm,preferably 15 to 45 µm, preferably 17.5 to 42.5 µm, preferably 20 to 40µm, preferably 21 to 39 µm, preferably 22 to 38 µm, preferably 23 to 37µm, preferably 24 to 36 µm, preferably 25 to 35 µm.In some embodiments,the polypropylene layer has a RMS surface roughness of 20 to 65 µm,preferably 22.5 to 62.5 µm, preferably 25 to 60 µm, preferably 27.5 to57.5 µm, preferably 30 to 55 µm, preferably 32.5 to 52.5 µm, preferably35 to 50 µm, preferably 36 to 49 µm.Such values of surface roughness(either RMS or Ra) would permit the polypropylene layer to be describedas “microtextured” as the surface comprises features smaller than or hasa surface roughness less than 500 µm.

The superhydrophobic asphalt may find use as a waterproofing materialitself or a component part of a waterproofing material. Such awaterproofing material may be used in roofing applications. Such awaterproofing material may be useful as a coating which is applied to aflat or curved surface. The superhydrophobic asphalt may also find useas paving material itself of a component part of a paving material. Sucha paving material may be used to pave, for example, roads, airportrunways, aprons, or ramps, walkways, stairs, or portions thereof. Thewaterproofing material and/or paving material may be useful for placingon surfaces symbols, writing, or other marks which are waterproof and/orsuperhydrophobic.

The examples below are intended to further illustrate protocols forpreparing and characterizing the superhydrophobic asphalt of the presentdisclosure and are not intended to limit the scope of the claims.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

EXAMPLES Preparation of Superhydrophobic Asphalt

An SBS modified asphalt substrate with performance grade of 76-10 wasused herein. Asphalt-SBS modification was achieved by hot blending 4% ofradial-type-SBS with performance grade 64-16 fresh asphalt binder at180° C., for 1 h at 3000 rpm. The choice of SBS modified asphalt assubstrate was due to its wide application in roofing and waterproofingindustry [K. Oba, and M. Hugener, Mater. Struct. 28 (9) (1995) 534-544].Basic properties of the SBS asphalt substrate are presented in Table 1.Flash point was obtained using Cleveland open-cup test [ASTM:D92-18,Standard Test Method for Flash and Fire Points by Cleveland Open CupTester., ASTM Int. West Conshohocken, PA. (2018)]. Viscosity wasmeasured using rotational viscometer [ASTM:D4402, Standard Test Methodfor Viscosity Determination of Asphalt at Elevated Temperatures Using aRotational Viscometer., ASTM Int. West Conshohocken, PA. (2015)]. Ringand ball method was used for softening point test [ASTM:D36, StandardTest Method for Softening Point of Bitumen (Ring-and-Ball Apparatus),ASTM Int. West Conshohocken, PA. (2014)]. Ductility test was accordingto ASTM D113 [ASTM:D113-17, Standard Test Method for Ductility ofAsphalt Materials, ASTM Int. West Conshohocken, PA. (2017)]. Thesaturate, aromatics, resins and asphaltene (SARA) compositions of thefresh asphalt were estimated to be 27.33%, 24.72%, 19.22%, and 28.73%respectively [ASTM:D4124-09, Standard Test Method for Separation ofAsphalt into Four Fractions, ASTM Int. West Conshohocken, PA. (2018)].

Table 1 Physical properties of SBS-modified asphalt substrate. SofteningPoint Viscosity at 135° C. Ductility at 25° C. Flash Point 86° C. 1612cP 14.5 cm 330° C.

Polypropylene waste was identified and collected from municipal wastebased on its recycled label #5. Disposable polypropylene plastic cupswere targeted and isolated from the waste. The collected plastic wastewas recycled by washing, drying, and cutting to produce recycledpolypropylene (RPP). The RPP was further milled to finer material havingsize of < 3 mm using a Universal Cutting Mill Pulverisette 19 (FRITSCH,Germany). An image of the processed and milled recycled polypropylene isshown in FIG. 2 . The milled RPP material was sieved to obtain twodifferent sizes using mesh #80 (177 mm) and #100 (149 mm). The firstsize passes sieve #80 and was retained on sieve #100, while the secondsize passes sieve #100. The first micronized RPP size was designated as#80 and the second as #100. Scanning Electron Microscopy (SEM) wasemployed to study the morphologies of the two micronized RPP materials(JSM-5800LV, JEOL, Japan), as provided in FIGS. 3A-3B. FIG. 3A shows themesh #80 micronized RPP and FIG. 3B shows the mesh #100 micronized RPP.Differential scanning calorimetry (DSC) was also used to characterizedthe micronized RPP with DSC Q1000 V9.4, USA. DSC test was run inNitrogen (N₂) environment, with 50 mL/min flowrate, using 3heat/cool/heat cycles at 10° C. heating and cooling rate [ASTM:D3418,Standard Test Method for Transition Temperatures and Enthalpies ofFusion and Crystallization of Polymers by Differential ScanningCalorimetry, ASTM Int. West Conshohocken, PA. (2015)].

FIG. 1 summarizes the preparation process of the micronized RPP-treatedasphalt surfaces. A thin layer (2 mm) of molten SBS modified asphaltbinder was first casted in a silicon mold. The asphalt was initiallymelted at 165° C. for a duration of approximately 40 min in an oven.Molten asphalt was stirred manually using metallic spatula for around 2to 3 min before casting the thin substrate layer. The 2 mm thick asphaltsubstrate was then transferred from the silicon mold to a 2 × 3 × 0.5 cmaluminum base after cooling. The surface of the asphalt substrate wasuniformly covered with a blanket of the micronized RPP (230 ± 15 g/m²)using a sieve. The set-up (asphalt-substrate on aluminum base coveredwith RPP) was put in an oven to cure at 100° C. The curing temperaturewas carefully selected to prevent excessive melting of the asphaltsubstrate. Samples were produced for three difference curing durations(25, 40, & 55 min) for each size of the micronized RPP. The initial 25min curing time was found to be the minimal time needed for meaningfulsurface coverage to be achieved at the curing temperature. At the end ofeach curing duration, samples were brought out to be cooled for at least10 min before blowing-off the surplus (unattached) micronized RPP. Allsamples were characterized and tested within 24 h after preparation.

Surface profile of the RPP-treated asphalt surfaces was analyzed using3D optical profilometer (Contour GT-K, Bruker, USA). Instruments andmeasurements for the surface profile were performed according to ISO25178 standard specifications part 1 to part 600. Water contact angle(WCA) of the surfaces was estimated using sessile drop video contactangle measurement system (VCA Optima, AST Products, USA). Standardprocedure and specifications adopted for WCA measurements are accordingto ASTM D7334 [ASTM:D7334-08, Standard Practice for Surface Wettabilityof Coating, Substrates and Pigments by Advancing Contact AngleMeasurement, (2013)]. A de-ionized water droplet (3mL) was used for WCAmeasurement at room temperature (23 ± 1° C.). At least 3 replicatemeasurements were taken at random spots on each sample for the WCA andsurface roughness parameter. SEM was used to study the morphology of theRPP-treated asphalt surface. This includes micronized-RPP asphaltbond-interface analysis. Short-term stability of the SHRPP-asphaltsurfaces was assessed by re-evaluating the WCA of the substrates after1-year exposure. Samples were exposed to environment with an annualaverage temperature of 24 ± 7.0° C., relative humidity of 55 ± 6.5%, anddaily sunlight of 8 ± 1 h respectively. Work of adhesion (WA) betweenthe water droplets and RPP-treated asphalt surfaces was estimated usingYoung’s equation given in Eq. (1) [M. Zakerzadeh, et. al., Constr.Build. Mater. 180 (2018) 285-290; and N.K. Adam, and H.K. Livingston,Nature 182 (1958) 128]. In Eq (1), cL represents the surface tension ofthe liquid phase, and θ the contact angle between the liquid and thesolid phase. Surface tension of de-ionized water at room temperature wastaken as 72.75 mNm⁻¹ [N.R. Pallas, and Y. Harrison, Colloids Surf. 43(2) (1990) 169-194].

WA = γ_(L)(1 + cos θ)

Characterization of Superhydrophobic Asphalt

FIG. 4 shows the surface microstructure of the untreated SBS-modifiedasphalt substrate. The SEM image of the surface revealed micro- ridgeand valley texture having zigzag-like orientation. Profile roughnessmeasurements indicated that the asphalt substrate surface has ArithmeticMean Deviation roughness (Ra) of 1.27 ± 0.77 mm, and Root Mean Squaredroughness (RMS) of 1.69 ± 1.14 mm. This placed the asphalt surface at N7roughness grade category based on International Organization forStandardization [ISO, Geometrical product specification (GPS)-Surfacetexture: Areal-Part 70: Material measures., Int. Organ. Stand. ISO 25178(2017)]. Because the average WCA of the asphalt surface was estimated tobe around 109.9 ± 0.9° (see sample result in FIG. 5A), the existingsurface profile and chemistry of the asphalt substrate was onlyhydrophobic. This WCA value qualifies the asphalt substrate to be wellwithin the hydrophobic class, and 35° away from being superhydrophobic.However, it has been established that a hydrophobic material with a WCAbetween 100°-120° could achieve superhydrophobicity with WCA of up to170° if successfully microtextured [Aurelie Lafuma, David Quéré, Nat.Mater. 2 (7) (2003) 457-460]. Recent previous studies have shown thatthis phenomena applies for asphalt binder if appropriately treated withthe right material [M.A. Dalhat, and A.Y. Adesina, Constr. Build. Mater.240 (2020); and M.A. Dalhat, and A.Y. Adesina, J. Mater. Civ. Eng. 31(2019) 4019229]. These past studies utilized micronized tire rubber andrecycled polyethylene waste, respectively, to achieve thesuperhydrophobic asphalt surface. Here, micronized RPP was used tosuccessfully transform the hydrophobic asphalt surface tosuperhydrophobic. The WCA of thin sheet of the unprocessed RPP surfacewas also measured, as shown in FIG. 5B. The WCA (59.4 ± 0.5°) of theunprocessed RPP sheet was observed to be within the hydrophilic range(<90° C.) [K.Y. Law, J. Phys. Chem. Lett. 5 (4) (2014) 686-688].

The SEM images of the micronized RPP passing mesh #80 and #100 are shownin FIGS. 3A and 3B respectively. Both powders showed elongated andrugged morphology having teared edges resulting from the millingprocess. As expected, the RPP powder passing mesh #80 showed lager grainsize than its counter-part (mesh #100). The sizes of the micronized RPPand their surface morphology are expected to influence the roughness andWCA of the asphalt substrate. Results of the thermal characterization ofthe RPP powder using differential scanning calorimetry are shown in FIG.6 . The two melting curves showed endothermic peaks just a little beyond160° C., indicating that the average melting point of the RPP isapproximately 162° C. This finding is in good agreement with previousstudies on the melting characteristics of virgin polypropylene [T.McNally, et. al., Polymer (Guildf). 43 (13) (2002) 3785-3793]. Theobserved melting temperature of the RPP indicates that the micronizedRPP should not be expected to undergo any significant change in shapeand size during curing at 100° C. Physical attachment/bonding will bemainly due to asphalt softening and sinking of the RPP particles.

Surface profile results of the RPP-treated asphalt substrates withrespect to Ra and RMS roughness parameter are presented in FIG. 7 . TheRa and RMS of the various RPP-treated asphalt surfaces increased up to40 min of curing duration. But beyond 40 min up to 55 min, roughness ofthe various surfaces stopped increasing. Asphalt surface treated withmesh #80 micronized RPP showed higher roughness than those treated withmesh #100 RPP. This observation is true for both Ra and RMS valuesobtained at different curing durations. Higher roughness of the asphaltsurfaces treated with mesh #80 RPP can be associated with the fact thatmesh #80 RPP powders have a bigger grain size than the mesh #100 RPP.Sample 3D surface profiles of the various RPP-treated asphalt surfacesare presented in FIGS. 8A-8F. The increase in the surface roughness withincrease in curing duration was due to micronized RPP adhering to theasphalt surface (see FIGS. 13A-13D). The amount of RPP adhering to theasphalt surface was observed to increase with increase in the curingduration, as shown in FIG. 9 . No significant difference in massaccumulation was observed between the mesh #80 RPP-treated asphaltsurfaces and those treated with mesh #100, indicating that the resultingdifference in observed surface roughness to be associated with thedifference in the sizes of the two micronized RPP powders. Continuousincrease in mass accumulation and non-increase in surface roughness from40 min to 55 min (see FIGS. 7 and 9 ) indicates that, some alreadyattached RPP sank deeper in to the asphalt substrate allowing otheradditional RPP particles to adhere to the asphalt substrate.

The average and maximum observed WCAs of the various asphalt surfacestreated with the micronized RPP are shown in FIG. 10 . In comparison tothe WCA of the asphalt substrate (110 °) and the RPP sheet (59 °) (seeFIGS. 4A-4B), the micronized RPP-treated asphalt surfaces showedsignificant increase in WCA. All the treated asphalt surfaces showed WCAsignificantly higher than the lower superhydrophobic limit of 145 °,making the various surfaces to exhibit superhydrophobic properties.Sample images of the maximum observed WCA of the various treated asphaltsubstrates are presented in FIGS. 11A-11F. In general, the average andmaximum WCA increases with increase in curing duration. This trend ismore obvious with respect to asphalt substrates that were treated withmesh #80 RPP. The asphalt surfaces treated with mesh #80 RPP showedhigher WCA than those treated with mesh #100 RPP powder. This could bebecause the asphalts treated with mesh #80 RPP showed higher surfaceroughness (see FIG. 7 ) and slightly higher mass-accumulation (see FIG.9 ) than the asphalt surfaces treated with mesh #100 RPP.

Results of the WCA before and after exposure are presented in FIG. 12 .Even the untreated asphalt substrate showed a slight loss of WCA afterthe 12-months exposure. This could be associated with loss of somevolatile/oily organic component in the asphalt that usually accompaniedshort-term aging [X. Lu, and U. Isacsson, Constr. Build. Mater. 16(1)(2002) 15-22]. The micronized RPP-treated asphalt surfaces also showedlower WCA after exposure, but asphalt substrates cured for longerduration showed lesser loss in WCA than those cured for shorterduration. The asphalt substrates cured for longer duration happened tohave higher accumulated mass of the micronized RPP than those cured forshorter duration (see FIG. 9 ). In addition, the micronized RPP on theasphalt substrates that were cured for longer duration are more likelyto be deeply rooted and adhere more effectively. Even after the 12months exposure, the 55 min cured asphalt substrates showed appreciableWCA margin above the lower superhydrophobic limit of 145 °. A similartrend of before and after exposure was observed in similar previousstudy involving asphalt surfaces treated with micronized recycledpolyethylene [M.A. Dalhat, and A.Y. Adesina, Constr. Build. Mater. 240(2020)].

Work of adhesion is defined as the energy per unit area required toseparate un-absorbed liquid from a solid surface [N.K. Adam, and H.K.Livingston, Nature 182 (1958) 128]. It is an energy parameter that givesa measure of anti-icing and water resistance of a given surface [T.Bharathidasan, et. al., Appl. Surf. Sci. 314 (2014) 241-250]. Results ofthe WA for the RPP-treated asphalt surfaces before and after exposureare summarized in Table 2. It can be observed that the RPP-treatedasphalt surfaces showed significantly lower WA values, relative to theuntreated asphalt surface. This signifies an improvement in waterresistance and higher anti-icing potential of the RPP-treated asphaltsurfaces. The WA decreases with increase in treatment duration, whichcorresponds to the increase in WCA previously observed (see FIG. 10 ).Approximately 86% and 83% estimated drop in WA were observed after 55min curing for mesh #80 and mesh #100 RPP surfaces respectively, beforeexposure. After exposure, the drop in WA for these surfaces are around71% and 73% respectively.

Table 2 Work of Adhesion on the various RPP-treated asphalt surfaces.All values have units of mNm⁻¹. Curing Time Mesh #80 Mesh #100 Beforeexposure After exposure Before exposure After exposure Untreated 47.71 ±0.35 49.87 ±0.37 47.71 ± 0.35 49.87 ± 0.37 25 min 8.15 ± 1.22 26.76 ±1.66 9.57 ± 1.03 17.87 ± 1.37 40 min 7.27 ± 2.18 14.37 ± 0.26 9.55 ±1.93 13.60 ± 0.80 55 min 6.50 ± 2.15 7.45 ± 0.29 8.28 ± 1.14 10.47 ±1.53

The surface morphology and asphalt-RPP interface of the RPP-treatedasphalt substrates cured at 55 min are shown in FIGS. 13A-13D. One majordifference between the mesh #80 treated asphalt surface in FIGS. 13A-13Band that of mesh #100 shown in FIGS. 13C-13D is the height of attachedRPP particles. The mesh #80 RPP particles being bigger and moreelongated were mostly attached to the asphalt surface perpendicularly asopposed to the mesh #100 RPP particles that mostly got attachedside-ways. This made the #80 micronized RPP asphalt surface to have abetter droplet suspension system. As a result, the asphalt substratestreated with mesh #80 RPP exhibited higher WCA than those treated withmesh #100 RPP. Observing the asphalt-RPP interface from FIGS. 13B & 13Drevealed that the RPP particulates (both mesh #80 and #100) were fullyembedded on to the asphalt substrate. The adhered micronized RPPresulted in micro-mountains on the asphalt surface at closer inspection(see FIGS. 13B & 13D). It also led to the increase in surface roughnessof the asphalt substrate previously observed in FIG. 7 . Embedment ofthe micronized RPP particulates resulted in stretching of asphaltsubstrate as well. This is obvious if the un-treated asphalt substrateshown in FIG. 3 is compared to that seen in FIGS. 13B and 13D. Thezigzag oriented micro-ridge and valley texture previously observed onthe asphalt substrate is now transformed in to smoother thin stretchedmarks that are linearly oriented towards the RPP particles. Thistransformation has a lot to do with the higher WCA observed for theRPP-treated asphalt surfaces, as compared to the untreated substrate.

The obtained results of WCA and surface profile were statisticallyanalyzed using analysis of variance. This was done to assess the extentto which the experimental variables influenced the studied parameters.MiniTab18TM was employed for statistical analysis at 5% level ofsignificance. Table 3 presents the statistical analysis of the surfaceprofile variables (Ra & RMS) vs. curing time and RPP size as factors.Abbreviations in the table include degree of freedom (DF), adjusted sumof square (Adj. SS), adjusted mean square (Adj. MS), Fisher’s statisticvalue (F-value), and P-value statistics. The curing duration andmicronized RPP size were found to have significant influence on thesurface roughness of the various treated asphalt substrates (P-value <0.05). This implies that the observed difference in surface roughnessbetween the mesh #80 and mesh #100 RPP-treated asphalt surfaces wasstatistically significant. However, there is insufficient statisticalevidence to conclude that the curing duration and the RPP size had aninteractive effect on the surface roughness parameters of theRPP-treated asphalts (P-value > 0.05).

Table 3 Analysis of variance results for surface roughness of RPPtreated asphalt. * indicates statistically significant factor (P-value <0.05). Response Factors DF Adj. SS Adj. MS F-value P-value Ra RoughnessCuring time 2 287.21 143.606 14.64 0.001 * Mesh Size 1 67.62 67.625 6.890.022* Interaction 2 36.06 18.028 1.84 0.201 Error 12 117.71 9.809 Total17 508.60 RMS Roughness Curing Time 2 614.39 307.200 13.91 0.001 * MeshSize 1 143.20 143.200 6.48 0.026* Interaction 2 57.46 28.730 1.30 0.308Error 12 265.02 22.090 Total 17 1080.07

Table 4 presents the statistical analysis of the WCA before and afterexposure as response, vs. curing duration and RPP size as factors.Before exposure, the curing duration did not show significant influenceon the WCA of RPP-treated asphalt substrates (P-value = 0.07 > 0.05).However, the curing time significantly affects the WCA of the varioustreated asphalt surfaces after the exposure (P-value < 0.05). It waspreviously observed that substrates cured for longer duration exhibitedlower loss of WCA after exposure, see FIG. 12 . Since the accumulatedmass of the RPP was found to be proportional to the curing duration, itimplies that treatments which will results in higher RPP massconcentration on the asphalt surface are more likely to yield durableRPP-asphalt surfaces. On the other hand, size of the RPP significantlyinfluences the WCA before and after the exposure (P-value < 0.05).Additionally, interactive effect of the curing duration and RPP size onthe WCA after exposure is found to be statically significant (P-value <0.001). This means that both parameters (size of the RPP and curingduration) are vital for establishing a good SH RPP-treated asphaltmembrane.

Table 4 Analysis of variance results for WCA of RPP treated asphaltsurfaces. * indicates statistically significant factor (P-value < 0.05).Response Factors DF Adj. SS Adj. MS F-value P-value WCA before exposureCuring time 2 87.931 43.966 2.88 0.070 Mesh Size 1 84.623 84.623 5.550.024* Interaction 2 6.783 3.391 0.21 0.810 Error 32 511.885 15.996Total 37 688.24 WCA after exposure Curing Time 2 992.61 496.307 63.03<0.001 * Mesh Size 1 41.22 41.22 5.23 0.032* Interaction 2 227.53113.766 14.45 <0.001 * Error 22 173.24 7.875 Total 27 1495.28

Statistical analysis of WA on the RPP-treated asphalt surfaces ispresented in Table 5. Both the RPP size and curing duration showedsignificant effect on the WA for the various RPP-treated asphaltsurfaces. This is found to be the case both before and after exposure.As previously observed in the case of WCA, there is also a significantinteractive effect between the RPP mesh size and the curing duration onthe WA. It can be seen that the significant increase in WCA is equallytranslated in to noticeable decline in WA.

Table 5 Analysis of variance results for WA of RPP treated asphaltsurfaces. * indicates statistically significant factor (P-value < 0.05).Response Factors DF Adj. SS Adj. MS F-value P-value WA before exposureCuring time 2 21.374 10.6869 3.39 0.042* Mesh Size 1 44.272 44.271614.06 <0.001 * Interaction 2 1.677 0.8386 0.27 0.767 Error 48 151.1873.1497 Total 53 221.577 WA after exposure Curing Time 2 623.63 311.81572.69 <0.001 * Mesh Size 1 39.9 39.896 9.3 0.006* Interaction 2 142.6371.314 16.63 <0.001 * Error 22 94.37 4.29 Total 27 957.73

1. A method of forming a superhydrophobic asphalt, the methodcomprising: applying a layer of polypropylene granules to a surface of apolymer modified asphalt to form an uncured coated asphalt; and curingthe uncured coated asphalt at 75 to 150° C. to form the superhydrophobicasphalt, wherein: the superhydrophobic asphalt comprises a polypropylenelayer disposed upon an asphalt layer; the superhydrophobic asphalt has awater contact angle of 145 to 170°; and the polypropylene granules aresubstantially free of fluoropolymers and have a maximum particle size of250 µm.
 2. The method of claim 1, wherein the polymer modified asphaltis an elastomer-type polymer modified asphalt.
 3. The method of claim 2,wherein the elastomer-type polymer modified asphalt is styrene-butadienestyrene (SBS)-modified asphalt.
 4. The method of claim 3, wherein thestyrene-butadiene-styrene is a radial styrene-butadiene-styrene and ispresent in an amount of 0.5 to 10 wt% based on a total weight of thestyrene-butadiene styrene (SBS)-modified asphalt.
 5. The method of claim2, further comprising mixing a non-polymer-modified asphalt having aperformance grade of 64-16 with 0.5 to 10 wt% of an elastomer typepolymer at 150 to 200° C. to form the elastomer-type polymer modifiedasphalt.
 6. The method of claim 1, wherein the polymer modified asphalthas a softening point of 80 to 95° C., a viscosity at 135° C. of 1575 to1650 cP, a ductility at 25° C. of 11.5 to 17.5 cm, a flash point of 300to 360° C., and a performance grade of 76-10.
 7. The method of claim 1,wherein the polypropylene granules are present in the uncured coatedasphalt in an amount of 185 to 275 g polypropylene granules per m² ofsurface of the polymer modified asphalt.
 8. The method of claim 1,wherein the polypropylene granules have a minimum particle size of 100µm.
 9. The method of claim 1, wherein the curing is performed for 15 to90 minutes.
 10. The method of claim 1, wherein the polypropylene layeris present in an amount of 50 to 125 g per m² of polymer modifiedasphalt layer.
 11. The method of claim 1, wherein the superhydrophobicasphalt has a work of adhesion of 1 to 15 mN/m.
 12. The method of claim1, wherein the polypropylene layer has a R_(a) surface roughness of 10to 50 µm.
 13. A superhydrophobic asphalt comprising: an asphalt layercomprising a polymer modified asphalt; and a polypropylene layercomprising polypropylene granules thermally fused onto the asphaltlayer, wherein: the superhydrophobic asphalt has a water contact angleof 145 to 170° and a R_(a) surface roughness of 10 to 50 µm; and thepolymer granules are substantially free of fluoropolymers and have amaximum particle size of 177 µm.
 14. The superhydrophobic asphalt ofclaim 13, wherein the polymer modified asphalt has a softening point of80 to 95° C., a viscosity at 135° C. of 1575 to 1650 cP, a ductility at25° C. of 11.5 to 17.5 cm, a flash point of 300 to 360° C., and aperformance grade of 76-10.
 15. The superhydrophobic asphalt of claim13, wherein the polymer modified asphalt is an elastomer-type polymermodified asphalt.
 16. The superhydrophobic asphalt of claim 15, whereinthe elastomer-type modified asphalt is styrene-butadiene styrene(SBS)-modified asphalt.
 17. The superhydrophobic asphalt of claim 16,wherein the styrene-butadiene-styrene is a radialstyrene-butadiene-styrene and is present in an amount of 0.5 to 10 wt%based on a total weight of the styrene-butadiene styrene (SBS)-modifiedasphalt.
 18. The superhydrophobic asphalt of claim 13, wherein thepolypropylene layer is present in an amount of 50 to 125 g per m² ofpolymer modified asphalt layer.
 19. The superhydrophobic asphalt ofclaim 13, which is substantially free of silanes and/or siloxanes. 20.The superhydrophobic asphalt of claim 13, having a work of adhesion of 1to 15 mN/m.